This invention generally relates to a stable aqueous metallic flake containing coating composition that utilizes a phosphated polymer. In particular, this invention is directed to a stable aqueous aluminum flake containing a coating composition that utilizes a segmented phosphated copolymer.
It is well known to use metallic flakes in coating compositions for imparting metallic glamour, particularly in exterior finishes applied on automobile and truck bodies. Though there are relatively few problems associated with the use of these metallic flakes in solvent based coating compositions, when utilized in waterborne coating compositions, the metallic flake, particularly aluminum flake, reacts with water and any acid constituents present in such coating compositions. As a result, the flake deteriorates and produces hydrogen gas, which is a potential safety hazard. Furthermore, finishes resulting from such coating compositions have a reduced brightness and glamour.
To avoid the foregoing problems, Frangou [U.S. Pat. No. 4,675,358 (1987)] and Antonelli et al. U.S. Pat. No. 5,104,922 (1992)] used phosphated linear random polymers in metallic flake containing coating compositions. The phosphated portion of the polymer provides passivation of the flake. Residual phosphorousic acid groups attached to the polymer are neutralized with an amine or an inorganic base to disperse the polymer into water. These polymers must be sufficiently hydrophobic to associate with the metallic flake, typically an aluminum flake whose surface is hydrophobic. However, it is very difficult to obtain a balance of properties with these polymers. If more passivation is needed for the flake, the phosphated hydrophobic portion of the polymer is increased but at the expense of the hydrophilic portion of the polymer which reduces the dispersibility of the polymer. On the other hand, if more dispersibility is needed, the phosphated hydrophobic portion of the polymer is reduced but the protection provided to the flake is reduced proportionately. As a result, the glamour in the long term is reduced. Thus, as these properties of passivation and dispersibility of the polymer have to be balanced against one another, it becomes very difficult to achieve an optimal balance and still produce acceptable glamour. Even though, aforedescribed phosphated polymers offer some improved protection to metallic flake pigments against the evolution of gases and exhibit some improvement in the stability of coating compositions formulated with metallic pigments, additional improvements in glamour for the resultant coatings are still desirable.
Thus, a polymeric dispersant is still needed for producing a stable aqueous metallic flake containing coating composition that protects the underlying substrate, suppresses the deterioration of the metallic flake and formation of gases, does not deteriorate on weathering, has compatibility with a variety of solvents used in aqueous coating compositions and still produces coatings having improved glamour over the aforedescribed prior art metallic flake containing coating compositions.
The present invention is directed to an aqueous metallic flake containing coating composition comprising:
metallic flakes and a neutralized phosphated segmented copolymer dispersed in an aqueous carrier, said neutralized segmented copolymer comprising a neutralized phosphated graft copolymer, neutralized phosphated block copolymer or a combination thereof, wherein
said graft copolymer comprises one or more nonionic hydrophilic segments attached at single terminal points to a hydrophobic segment, and said block copolymer comprises one or two of nonionic hydrophilic segments linearly attached to a hydrophobic segment, wherein
a molar ratio of said hydrophobic segment to said nonionic hydrophilic segment in said graft and block copolymers varies in the range of from 96:4 to 4:96 and wherein said nonionic hydrophilic segment is polymerized from one or more nonionic monomers selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, vinyl pyrolidone, oxazoline, hydroxyethyl (meth)acrylate and a combination thereof; and
wherein said segmented phosphated copolymer is provided in the range of from 0.4 weight percent to 12 weight percent with phosphate moieties, all percentages being based on composition solids.
The present invention is also directed to a method for procucing aqueous metallic flake containing coating coposition comprising:
preparing a segmented copolymer comprising a graft copolymer, block copolymer or a combination thereof,
wherein said graft copolymer is prepared by:
polymerizing one or more ethylenically unsaturated monomers, one or more phosphate moiety reactive monomers and one or more nonionic macromonomers terminated with a polymerizable double bond to produce said graft copolymer having a hydrophobic segment with one or more nonionic hydrophilic segments attached at single terminal points thereto, said hydrophobic segment having one or more phosphate reactive moieties positioned thereon, said nonionic macromonomer being selected from the group consisting of polyethylene glycol monomethacrylate methyl ether, polypropylene glycol monomethacrylate methyl ether, polybutylene glycol monomethacrylate methyl ether, polyvinyl pyrolidone, polyoxazoline, polyhydroxyethyl methacrylate and a combination thereof, and wherein a molar ratio of said hydrophobic segment to said nonionic hydrophilic segment in said graft copolymer varies in the range of from 96:4 to 4:96:
wherein said block copolymer is prepared by:
polymerizing one or more of nonionic monomers selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, vinyl pyrolidone, oxazoline and hydroxy ethyl (meth)acrylate, one or more phosphate moiety reactive monomers and one or more ethylenically unsaturated macromonomers to produce said block copolymer having a hydrophobic segment with one or two nonionic hydrophilic segments linearly attached thereto, said hydrophobic segment having one or more phosphate reactive moieties positioned thereon and wherein a molar ratio of said hydrophobic segment to said nonionic hydrophilic segment in said block copolymer varies in the range of from 96:4 to 4:96;
contacting orthophosphoric acid, phosphorus pentoxide, a phosphorus compound containing xe2x80x94Oxe2x80x94PO(OH)2 group, or a combination thereof with said segmented copolymer to provide said segmented copolymer with one or more said phosphate moieties thereon;
neutralizing said phosphate moieties on said segmented copolymer by contacting with a neutralizing agent to produce a neutralized phosphated segmented copolymer; and
mixing metal flakes with said neutralized phosphated segmented copolymer in an aqueous carrier to produce said aqueous metallic flake containing coating composition.
One of the advantages of the coating composition of the present invention is that a coating resulting therefrom has improved glamour when compared against the glamour of coatings obtained from conventional waterborne metallic flake containing coating compositions.
Another advantage of the present invention is the flexibility it affords to the formulator in selecting from a wide variety of solvents, especially from the HAPs-free (hazardous air pollutants) solvents, in formulating the composition. As a result, the formulator, especially in the United States, is in a better position to meet the increasingly stringent legal requirements that deal with the acceptable level of release of VOC (volatile organic content) in the atmosphere.
Still another advantage of the present invention is the flexibility it affords to the formulator in selecting from a wide variety of metallic flakes, such as non-passivated or pre-passivated metallic flakes. As a result, the formulator has greater freedom in tailoring the resulting coating composition having desired coating properties, such as, for example, etch and mar resistance.
Yet another advantage of the novel aqueous metallic coating composition of the present invention is its improved dispersibility under a variety of loading requirements, such as higher metallic flake loading.
The novel aqueous metallic coating composition of the present invention also advantageously permits the formulator to select from a wider selection of other film forming polymers that can be incorporated in the coating composition.
As defined herein:
xe2x80x9cGlamourxe2x80x9d relates to the reflectance of a metallic flake containing coating when viewed from different angles, i.e., directional reflectance. One aspect of glamour is the reflectance of the coating when measured at the Near-Specular angle. The reflectance at this angle is called the Head-On-Brightness. Another aspect of glamour is how the reflectance changes between the Near-Specular and Far-From-Specular angles. This change in the reflectance is known as xe2x80x9cflopxe2x80x9d , xe2x80x9cflip-flopxe2x80x9d , xe2x80x9cflashxe2x80x9d , xe2x80x9cside-tonexe2x80x9d or xe2x80x9ctravelxe2x80x9d. Thus, glamour is reported in a number of ways, all relating to the spectrophotometric measurements of a metallic coating taken at various angles of reflectance. The process and the measurement device utilized for determining glamour are described in the U.S. Pat. No. 4,479,718, which is incorporated herein by reference. The higher the reported reading, the better is the glamour of the coating.xe2x80x9d
xe2x80x9cDispersibilityxe2x80x9d relates to the robustness of the stability of metal flakes to stay dispersed, i.e., not gel, in an aqueous carrier of a coating composition under various application conditions and also in the presence of various additives typically added to the coating composition for attaining desired coating properties. xe2x80x9cMetallic coatingxe2x80x9d or xe2x80x9ccoatingxe2x80x9d means a cured film of desired thickness on a substrate surface obtained from the application of a layer, typically through a spray nozzle, of an aqueous metallic coating composition.
xe2x80x9c(Meth)acrylicxe2x80x9d means methacrylic and acrylic.
xe2x80x9cPolymer solidsxe2x80x9d or xe2x80x9ccomposition solidsxe2x80x9d means a polymer or composition in its dry state.
xe2x80x9cGPC weight average (Mw) or GPC number average (Mn) molecular weightxe2x80x9d means Mw and Mn molecular weights of polymers obtained by using gel permeation chromatography utilizing polystyrene as the standard and tetrahydrofuran as the carrier solvent.
xe2x80x9cGraft copolymerxe2x80x9d means a segmented copolymer having one or more polymeric segments attached to each other, such as hydrophobic A and hydrophilic B segments illustrated in the following figures, wherein segment B results from a macromonomer having a single polymerizable double bond:
xe2x80x9cBlock copolymerxe2x80x9d means a segmented copolymer having one or more 
polymeric segments substantially linearly attached to each other, such as hydrophobic A and hydrophilic B segments illustrated in the following figures:
xe2x80x9cPassivated metallic flakexe2x80x9d means a metallic flake that has been treated or 
coated to reduce the chemical reactivity of its surface. The term xe2x80x9cpre-passivated metal flakesxe2x80x9d means metal flakes that had been passivated before they are added to a coating composition. The term xe2x80x9cnon-passivated metal flakesxe2x80x9d means metal flakes that had not been subjected to passivation before addition to a coating composition.
xe2x80x9cWater miscible solventsxe2x80x9d are those solvents that are completely or substantially soluble in water.
xe2x80x9cWater reducible solventsxe2x80x9d are those solvents that require co-solvent(s) for dissolving them in water.
xe2x80x9cSolubility parameterxe2x80x9d relates to a degree to which a hydrophobic segment in a copolymer partially dissolves in water. Thus, hydrophobic monomers having solubility parameters lower than those monomers having relatively higher solubility parameters would produce a hydrophobic segment that is relatively less soluble. Applicants have discovered that by making the use of the solubility parameter of the hydrophobic segment in a segmented copolymer, formulator can choose from a wider selection of metallic flakes that can be incorporated in a metallic paint. Thus, by lowering the solubility parameter of a hydrophobic segment, which is accomplished by selecting a mix of monomers having lower solubility parameters, the hydrophobicity of the resulting hydrophobic segment can be lowered. As a result, the formulator can achieve an optimal balance of the hydrophobic/hydrophylic segements suitable for use with non-passivated, pre-passivated metallic flakes or a combination thereof, as metallic flakes in the coating composition. Solubility parameters of monomers and polymers are known and can be obtained from several sources, such as, for example, from Solubility Parameter Values by E. Grulke in the Polymer Handbook, 3rd Edition (1989), edited by J. Brandrup and E. H. Immergut (publisherxe2x80x94John Wiley and Sons, New York, N.Y.) or from Handbook of Polymer-Liquid Interaction Parameters and Solubility Parameters by Allan F. M. Barton, 1990 edition (publisherxe2x80x94CRC Press, Boca Raton, Fla.).
The novel aqueous metallic coating composition of the present invention includes a neutralized segmented copolymer and metallic flakes. The applicants have unexpectedly discovered that the novel neutralized segmented copolymer of the present invention not only provides a stable waterborne coating composition but it also improves the glamour of the resultant coating when compared to conventional metallic coating. Moreover, the neutralized segmented copolymer of the present invention is compatible with a wide variety of film forming polymer binders, especially acrylic polymers, widely used in waterborne coatings.
The GPC weight average molecular weight of the neutralized segmented copolymer varies in the range of from 2,000 to 100,000, preferably in the range of from 10,000 to 40,000, more preferably in the range of from 5,000 to 30,000.
The neutralized phosphated segmented copolymer includes a neutralized phosphated graft copolymer, neutralized phosphated block copolymer or a combination thereof. When used as a combination, the neutralized phosphated segmented copolymer includes in the range of from 1 weight percent to 99 weight percent and more preferably in the range of from 70 weight percent to 90 weight percent of the graft copolymer, the remainder being the block copolymer, all weight percentages being based on the weight of copolymer solids. The neutralized phosphated graft copolymer is preferred.
The neutralized graft copolymer includes one or more nonionic hydrophilic segments attached at single terminal points to a hydrophobic segment and the neutralized block copolymer includes one or two nonionic hydrophilic segments linearly attached to one or at both terminal ends of a hydrophobic segment. The xe2x80x9chydrophobicxe2x80x9d (repelling, tending not to combine with, or incapable of dissolving in water) segment is relatively more hydrophobic than the xe2x80x9chydrophilicxe2x80x9d (having an affinity for water, readily absorbing or dissolving in water) nonionic segment. It is believed that the novel hydrophobic/hydrophilic segments of the segmented copolymer of the present invention provide maximum passivation of the flake, while still adequately dispersing the flakes and forming a stable aqueous coating composition.
The molar ratio of the hydrophobic segments to hydrophilic nonionic segments in both block and graft copolymers varies in the range of from 96:4 to 4:96, preferably in the range of from 85:15 to 15:85, more preferably in the range of from 80:20 to 20:80 and most preferably at 22:78.
The nonionic hydrophilic segment of the graft copolymer may be a nonionic macromonomer terminated with a polymerizable double bond to which the hydrophobic segment can be attached. Some of the suitable nonionic macromonomers terminated with a polymerizable double bond include polyethylene oxide, polypropylene oxide, polybutylene oxide, polyvinyl pyrolidone, polyoxazoline, polyhydroxyethyl methacrylate or a combination thereof. Polyhydroxyethyl methacrylate may be a homopolymer or a copolymer polymerized from a hydroxyethyl methacrylate monomer and one or more methacrylic monomers. The molecular weight of the nonionic macromonomer varies in the range of from 250 to 10,000, preferably from 500 to 3000 and more preferably from 550 to 2000. Suitable nonionic macromonomers terminated with a polymerizable double bond are commercially available. For example, Bisomer S 20W polyethylene glycol monomethacrylate methyl ether is available from Laporte Performance Chemicals. The nonionic hydrophilic segment of the block copolymer results from polymerizing one or more nonionic monomers selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, vinyl pyrolidone, oxazoline, hydroxyethyl (meth)acrylate and a combination thereof. Ethylene oxide is preferred. The nonionic hydrophilic segment results from a polymer having a GPC weight average molecular weight in the range of from 250 to 10,000, preferably from 500 to 3000 and more preferably from 550 to 2000.
Some of the monomers suitable for polymerizing the hydrophobic segment include alkyl (meth)acrylates having 1-18 carbon atoms in the alkyl group, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethyl hexyl (meth)acrylate, nonyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate; cycloaliphatic (meth)acrylates, such as trimethylcyclohexyl (meth)acrylate, and isobutylcyclohexyl (meth)acrylate; aryl (meth)crylates, such as benzyl (meth)acrylate. Other polymerizable monomers that can be used are isobornyl (meth)acrylate, styrene, alpha methyl styrene, methacrylamide and methacrylonitrile. Various combinations of the foregoing monomers are also suitable.
The segmented copolymer is further provided with phosphorous moieties in the range of from 0.4 weight percent to 12 weight percent, preferably in the range of from 0.8 weight percent to 9.0 weight percent and more preferably in the range of from 1.2 weight percent to 6.0 weight percent, all percentages being based on composition solids. The phosphorous moieties can be provided on either the hydrophobic or hydrophilic segments, or on both. Phosphorous moieties positioned on the hydrophobic segment are preferred. The phosphorous moiety passivates the metallic flakes, thereby substantially reducing the formation of gas, such as hydrogen, produced when aluminum flakes are used in aqueous coating compositions. Some of the suitable phosphorous moieties include those having at least one reactive oxygen, such as the one in a hydroxyl group. Phosphate moiety is preferred.
The metallic flakes and the neutralized segmented copolymer of the coating composition are dispersed in an aqueous carrier. The aqueous carrier includes water and generally includes one or more solvents, which may be water soluble, water reducible solvents or a combination thereof. The amount of solvent added to the coating composition is adjusted to provide the composition with a VOC (volatile organic content) in the range the range of from 0.1 kilograms (1.0 pounds per gallon) to 0.5 kilograms (4.0 pounds per gallon), preferably 0.3 kilograms (2.6 pounds per gallon) to 0.43 kilograms (3.6 pounds per gallon) and more preferably 0.34 kilograms (2.8 pounds per gallon) to 0.4 kilograms (3.4 pounds per gallon) of the solvent per liter of the coating composition. Some of the suitable solvents include C1 to C12 mono and di-alcohols, such as, for example, isopropanol, ethanol, methanol, butanol, 2-ethylhexanol and dodecanol. Tetrahydrofuran, glycol ethers and glycol ether acetates are also suitable. Other solvents include toluene, hexane, butyl cellosolve, butyl cellosolve acetate, carbitol. Some of the solvents, for example, propylene glycol monomethyl ether, ethylene glycol hexyl acetate, ethylene glycol n-butyl ether, dipropylene glycol and methyl ether acetate are available from Dow Chemical Company, Midland, Mich. Isopropanol, methyl ethyl ketone and acetone are preferred. If required and in order to reduce the HAPs, HAPs-free solvents, such as ethanol, butanol, butyl acetate, isobutanol, acetone, diacetone alcohol, methyl amyl alcohol, cyclohexanone, primary amyl acetate, methyl amyl ketone, 2-ethyl hexanol, propanol, ethyl acetate, tetrahydrofuran, isopropyl acetate, 2-ethyl hexyl acetate, ethyl 3-ethoxy propionate, pentyl propionate, ethanol, n-butyl propionate, tertiary butyl alcohol and 1-pentanol are most suitable.
Typically the aqueous carrier includes suitable amounts of minor components including non-alcohols, such as mineral spirits of various boiling point ranges. If desired suitable amounts of aromatic solvents such as, toluene, xylene and Solvesol 100, and nitro paraffins, such as 1-nitropropane and 2-nitropropane, can be added in small amounts.
The segmented copolymer having phosphorous moieties in the aqueous carrier is then neutralized with one or more neutralizing agents for aiding dispersion. Some of the suitable neutralizing agents include an inorganic base, an amine or a combination thereof. Suitable inorganic bases include alkali metal halide, preferably sodium hydroxide, and ammonium hydroxide. Ammonium hydroxide is preferred as an inorganic base. Suitable amines include amino methyl propanol, amino ethyl propanol, dimethyl ethanol amine and triethylamine. Amino methyl propanol and dimethyl ethanol amine are preferred.
Typically, the amount of metallic flakes added to the coating composition depends upon the degree of glamour desired. Generally, the coating composition includes in the range of from 0.1 weight percent to 40 weight percent, preferably in the range of from 1.0 weight percent to 20 weight percent of metallic flakes, all percentages being based on total composition solids. Some of the suitable metallic flakes include aluminum, bronze, nickel, and stainless steel. Metallic flakes, suitable for use in the present invention may pre-passivated or non-passivated. Aluminum flakes are preferred. Aluminum flakes suitable for use in the present invention include SS, SSP, TF, SIII grades supplied by Silberline Manufacturing Company, Brecksville, Ohio; TRC, WJD grades supplied by Toyal Americal, Inc., Lockport, Ill.; and Hydrolac(copyright) aluminum flakes supplied by Eckert America, Louisville, Ky. If desired, the coating composition can include pearlescent flakes and coated mica flakes, such as mica flakes coated with finely divided titanium dioxide.
Applicants have unexpectedly discovered that by controlling the molar ratio of the hydrophobic segment to the nonionic hydrophilic segment in the segmented copolymer, the formulator is afforded the freedom to utilize various types of metallic flakes without destroying the dispersibility of the resulting coating composition or generating unacceptable levels of hydrogen that typically result when non-passivated aluminum flakes are dispersed in aqueous coating compositions. As a result, the formulator is provided more flexibility in fine tuning the blending of the aqueous carrier that meets the customer requirements.
Thus, by including a neutralized segmented copolymer in the coating composition to assist in the flake dispersion, an optimum coating composition can be formed to provide maximum passivation of the flake, adequately disperse the flake and still form a stable aqueous coating composition.
In addition to the metallic flake, the coating composition of the present invention may include any of the conventional pigments typically used in waterborne paints, such as metallic oxides, including titanium dioxide, iron oxides of various colors, zinc oxide, carbon black; filler pigments such as, talc, china clay, barytes, carbonates, silicates; and a wide variety of organic pigments such as, quinacridones, phthalocyanines, perylenes, azo pigments, indanthrones, carbazoles such as, carbazole violet, isoindolinones, isoindolones, thioindigo reds, and benzimidazolinones. It may be desirable to add other optional ingredients to the coating composition, such as antioxidants; flow control agents; rheology control agents, such as fumed silica and non-aqueous dispersions (NADs); UV stabilizers; UV screeners, quenchers and absorbers.
Under some circumstances, it may be desirable to form coating compositions that do not contain metallic flakes but contain any of the aforementioned non-metallic flakes. Though such non-metallic flakes do not require passivation, it is still expected and contemplated that the neutralized phosphated segmented copolymer of the present invention would provide excellent dispersibility to such a coating composition containing non-metallic flakes.
As stated earlier, the segmented copolymer may be a graft copolymer, block copolymer or a combination thereof. The processes described below can be employed to produce the graft copolymer and the block polymer.
The nonionic macromonomers, such as polyethylene, polypropylene, polybuylene glycol monomethacrylate methyl ethers are available commercially, for example, International Specialty Chemicals, United Kingdom and Laporte Performance Chemicals.
The following method describes one way to make nonionic macromonomers containing hydroxyethyl methacrylate:
In the preparation of the nonionic macromonomer to ensure that the resulting macromonomer has only one terminal double bond which will polymerize with the hydrophobic monomers to form the graft copolymer, the macromonomer is polymerized by using a catalytic cobalt chain transfer agent that preferably contains a Co+2 or Co+3 group. Typically, in the first step of the process for preparing the macromonomer, the aforedescribed nonionic monomers are mixed with an inert organic solvent and a cobalt chain transfer agent and heated usually to the reflux temperature of the reaction mixture. In subsequent steps additional monomers and cobalt catalyst and conventional azo polymerization catalyst such as, 2,2xe2x80x2-azobis(2-methylbutanenitrile) and 2,2xe2x80x2-azobis(2,4xe2x80x2-dimethylpentanenitrile) 2,2xe2x80x2-azobis(2,4-dimethyl-4-methoxyvaleronitrile) are added and polymerization is continued at about 100xc2x0 C. to 135xc2x0 C. for about 4 to 8 hours until a macromonomer of a desired molecular weight is formed. Preferably, the inert organic solvent is then stripped off. Preferred cobalt chain transfer agents or catalysts are described in U.S. Pat. No. 4,680,352 to Janowicz et al and U.S. Pat. No. 4,722,984 to Janowicz and WO 87/03605, hereby incorporated by reference in their entirety. Most preferred are pentacyanocobaltate (II or III), diaquabis(borondifluorodimethyl-glyoximato) cobaltate(II or III) and diaquabis(borondifluorophenylglyoximato) cobaltate (II or III). Typically these chain transfer agents are used at concentrations of about 5 to 1000 ppm (parts per million) based on the monomers used.
One of the ways, the graft copolymer suitable for use in the present invention is prepared is by polymerizing one or more of the aforedescribed ethylenically unsaturated monomers and one or more phosphorous moiety reactive monomers in an inert organic solvent and in the presence of the aforedescribed nonionic macromonomers and a polymerization catalyst, such as any of the aforementioned azo catalyst or other suitable catalysts such as, peroxides and hydroperoxides. Typical of such catalyst are di-tertiary butyl peroxide, di-cumylperoxide, tertiaryamyl peroxide, cumenehydroperoxide, di(n-propyl) peroxydicarbonate, peresters such as, amyl peroxyacetate and t-butyl peracetate. Some of the phosphorous moiety reactive monomers suitable for use in the present invention include glycidyl (meth)acrylate. Glycidyl methacrylate is preferred. The amount of phosphorous moiety reactive monomer added to the reaction mixture is adjusted to provide the graft copolymer with the desired level of phosphorous moieties and the amount of ethylenically unsaturated monomers and macromonomers added to the reaction mixture is adjusted to achieve the desired molar ratio of the hydrophobic segment to the nonionic hydrophilic segment. Polymerization is continued at about 100xc2x0 C. to 135xc2x0 C. for about 4 to 8 hours, usually at the reflux temperature of the reaction mixture, until a graft copolymer is formed having the desired molecular weight.
The graft copolymer having the phosphate reactive moieties, such as glycidyl moieties, is then reacted preferably with a 1:1 molar equivalent amount of orthophosphoric acid (H3PO4), phosphoric acid, phosphorus pentoxide P2O5 or other phosphorus compounds which contain the grouping xe2x80x94Oxe2x80x94PO(OH)2, such as, for example pyrophosphoric acid (H4PO7) to provide the graft polymer with phosphate moieties. The reaction is continued at about 50xc2x0 C. to 70xc2x0 C. for 4 to 6 hours or until all the glycidyl moieties are reacted. The extent of reaction can be determined by making acid number measurements.
The phosphated graft copolymer is then neutralized with the aforedescribed neutralizing agent and mixed with a desired amount of the metallic flake. Conventional mixing is used to form the dispersion. Often an associate thickener is added to aid in formation of a stable dispersion.
Another way to introduce phosphate groups into the graft copolymer is to form a polymer having reactive hydroxyl group, such as for example, by forming the graft copolymer with hydroxy alkyl methacrylates or acrylates and subsequently reacting the hydroxy groups with phosphorus pentoxide and neutralizing phosphoric acid groups with amine or inorganic)ase described earlier.
Then, one of the processes that can be used for producing the block copolymer is as follows:
As a first step, ethylenically unsaturated macromonomers having a GPC weight average molecular weight in the range of from 250 to 10,000, preferably from 500 to 3000 and more preferably from 550 to 2000 are produced.
One or more of nonionic monomers selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, vinyl pyrolidone, oxazoline and hydroxy ethyl (meth)acrylate, one or more of the phosphorous moiety reactive monomers are preferably added to an inert organic solvent and then one or more of the ethylenically unsaturated macromonomers are added to the polymer mixture to produce the block copolymer having a hydrophobic segment with one or two nonionic hydrophilic segments linearly attached thereto. The hydrophobic segment has one or more phosphorous reactive moieties positioned thereon and the molar ratio of the hydrophobic segment to the nonionic hydrophilic segment in the block copolymer varies in the range of from 96:4 to 4:96, preferably in the range of from 85:15 to 15:85, more preferably in the range of from 75:25 to 25:75 and most preferably at 22:78.
A number of parameters can be adjusted with the segmented copolymer to form an optimum dispersant. The molar ratio of the hydrophobic segment to the nonionic hydrophilic segment can be adjusted, the GPC weight average molecular weight of the hydrophobic segment can be increased or decreased, the number phosphorous moieties of the segmented copolymer disposed on either the hydrophilic segment or the hydrophobic segment can be adjusted as needed to provide optimum passivation and dispersibility. By using the segmented copolymer, a substantially wider range of copolymers can be formulated that balance, hydrophilicity and hydrophobicity and phosphate content of the graft copolymer to form superior dispersions and coating compositions by comparison to the conventional coating compositions.
Particularly useful aqueous metallic flake containing coating composition suitable for using pre-passivated aluminum flakes includes a graft copolymer having a hydrophobic segment of polymerized monomers of styrene/methyl methacrylate/butyl acrylate/glycidyl methacrylate in weight ratios of 20/25/35/20, 30/20/30/20 and 20/25/35/20 and having a weight average molecular weight in the rang of 14,000 to 18,000. The nonionic hydrophilic segment of the graft copolymer results from polyethylene glycol monomethacrylate methyl ether. The glycidyl groups of the copolymer are reacted with phosphorousic acid on a 1/1 molar equivalent basis.
Applicants have unexpectedly discovered that by controlling the molar ratio and the hydrophobicity of the hydrophobic segment, expressed as solubility parameter, the formulator can select from a wide range of the metallic flakes. Thus, when a segmented copolymer having the molar ratio above 65:35 and the solubility parameter below 8.9 is used, the coating composition can include pre-passivated, non-passivated aluminum flakes or a combination thereof. The preferred solubility parameter herein is in the range of 7.8 to 8.6, more preferably in the range from 8.4 to 8.6.
When a segmented copolymer having the molar ratio below 65:35 and the solubility parameter above 8.9 is used, the coating composition can include pre-passivated flakes, more particularly pre-passivated aluminum flakes. The preferred solubility parameter herein is in the range of 9.3 to 11, more preferably in the range from 9.3 to 9.4. Even though the formulator has fewer options with respect to the type of metallic flakes that can be used, by using relatively less hydrophobic segment, the dispersibility of the coating composition can be improved. As a result, the formulator has more choices of additives that can be added to the coating compositions.
The coating composition of the present invention can be used in a variety of ways, such as topcoats which may be monocoats or basecoats of a clearcoat/basecoat finish and may also be added to primers and primer surfacers. These compositions preferably have an acrylic polymer as the film forming constituent and may contain crosslinking agents, such as blocked isocyanate, alkylated melamines, and epoxy resins. Other suitable film forming polymers include acrylourethanes, polyesters and polyester urethanes, polyethers and compatible polyether urethanes. It is desirable to have the film-forming polymer of the coating composition substantially structurally similar to the neutralized phosphated segmented copolymer so that during curing, the film-forming polymer will cure at a substantially the same rate as the segmented copolymer thereby preventing striation of the resultant coating.
The metallic flake containing coating composition of the present invention is most suitable for use as an automotive paint in OEM (original equipment manufacturer) automotive settings or as an automotive refinish paint typically used in making repairs and touch-ups to automotive bodies. Obviously, the paint is also well suited for use in other applications such as coating truck bodies, boats, airplanes, tractors, cranes and other metal bodies. If desired, the coating composition of the present invention can be also used on non-metallic surfaces, such as wood and plastic, for example RIM (reaction injection molded) auto bumpers.
The following examples illustrate the invention.